proptest/array.rs
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//-
// Copyright 2017 Jason Lingle
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Support for strategies producing fixed-length arrays.
//!
//! An array of strategies (but only length 1 to 32 for now) is itself a
//! strategy which generates arrays of that size drawing elements from the
//! corresponding input strategies.
//!
//! See also [`UniformArrayStrategy`](struct.UniformArrayStrategy.html) for
//! easily making a strategy for an array drawn from one strategy.
//!
//! General implementations are available for sizes 1 through 32.
use core::marker::PhantomData;
use crate::strategy::*;
use crate::test_runner::*;
/// A `Strategy` which generates fixed-size arrays containing values drawn from
/// an inner strategy.
///
/// `T` must be an array type of length 1 to 32 whose values are produced by
/// strategy `S`. Instances of this type are normally created by the various
/// `uniformXX` functions in this module.
///
/// This is mainly useful when the inner strategy is not `Copy`, precluding
/// expressing the strategy as `[myStrategy; 32]`, for example.
///
/// ## Example
///
/// ```
/// use proptest::prelude::*;
///
/// proptest! {
/// #[test]
/// fn test_something(a in prop::array::uniform32(1u32..)) {
/// let unexpected = [0u32;32];
/// // `a` is also a [u32;32], so we can compare them directly
/// assert_ne!(unexpected, a);
/// }
/// }
/// # fn main() { }
/// ```
#[must_use = "strategies do nothing unless used"]
#[derive(Clone, Copy, Debug)]
pub struct UniformArrayStrategy<S, T> {
strategy: S,
_marker: PhantomData<T>,
}
impl<S, T> UniformArrayStrategy<S, T> {
/// Directly create a `UniformArrayStrategy`.
///
/// This is only intended for advanced use, since the only way to specify
/// the array size is with the turbofish operator and explicitly naming the
/// type of the values in the array and the strategy itself.
///
/// Prefer the `uniformXX` functions at module-level unless something
/// precludes their use.
pub fn new(strategy: S) -> Self {
UniformArrayStrategy {
strategy,
_marker: PhantomData,
}
}
}
/// A `ValueTree` operating over a fixed-size array.
#[derive(Clone, Copy, Debug)]
pub struct ArrayValueTree<T> {
tree: T,
shrinker: usize,
last_shrinker: Option<usize>,
}
/// Create a strategy to generate fixed-length arrays.
///
/// All values within the new strategy are generated using the given
/// strategy.
///
/// See [`UniformArrayStrategy`](struct.UniformArrayStrategy.html) for
/// example usage.
pub fn uniform<S: Strategy, const N: usize>(
strategy: S,
) -> UniformArrayStrategy<S, [S::Value; N]> {
UniformArrayStrategy {
strategy,
_marker: PhantomData,
}
}
macro_rules! small_array {
($n:tt $uni:ident) => {
/// Create a strategy to generate fixed-length arrays.
///
/// All values within the new strategy are generated using the given
/// strategy. The length of the array corresponds to the suffix of the
/// name of this function.
///
/// See [`UniformArrayStrategy`](struct.UniformArrayStrategy.html) for
/// example usage.
pub fn $uni<S: Strategy>(
strategy: S,
) -> UniformArrayStrategy<S, [S::Value; $n]> {
UniformArrayStrategy {
strategy,
_marker: PhantomData,
}
}
};
}
impl<S: Strategy, const N: usize> Strategy for [S; N] {
type Tree = ArrayValueTree<[S::Tree; N]>;
type Value = [S::Value; N];
fn new_tree(&self, runner: &mut TestRunner) -> NewTree<Self> {
Ok(ArrayValueTree {
tree: unarray::build_array_result(|i| self[i].new_tree(runner))?,
shrinker: 0,
last_shrinker: None,
})
}
}
impl<S: Strategy, const N: usize> Strategy
for UniformArrayStrategy<S, [S::Value; N]>
{
type Tree = ArrayValueTree<[S::Tree; N]>;
type Value = [S::Value; N];
fn new_tree(&self, runner: &mut TestRunner) -> NewTree<Self> {
Ok(ArrayValueTree {
tree: unarray::build_array_result(|_| {
self.strategy.new_tree(runner)
})?,
shrinker: 0,
last_shrinker: None,
})
}
}
impl<T: ValueTree, const N: usize> ValueTree for ArrayValueTree<[T; N]> {
type Value = [T::Value; N];
fn current(&self) -> [T::Value; N] {
core::array::from_fn(|i| self.tree[i].current())
}
fn simplify(&mut self) -> bool {
while self.shrinker < N {
if self.tree[self.shrinker].simplify() {
self.last_shrinker = Some(self.shrinker);
return true;
} else {
self.shrinker += 1;
}
}
false
}
fn complicate(&mut self) -> bool {
if let Some(shrinker) = self.last_shrinker {
self.shrinker = shrinker;
if self.tree[shrinker].complicate() {
true
} else {
self.last_shrinker = None;
false
}
} else {
false
}
}
}
small_array!(1 uniform1);
small_array!(2 uniform2);
small_array!(3 uniform3);
small_array!(4 uniform4);
small_array!(5 uniform5);
small_array!(6 uniform6);
small_array!(7 uniform7);
small_array!(8 uniform8);
small_array!(9 uniform9);
small_array!(10 uniform10);
small_array!(11 uniform11);
small_array!(12 uniform12);
small_array!(13 uniform13);
small_array!(14 uniform14);
small_array!(15 uniform15);
small_array!(16 uniform16);
small_array!(17 uniform17);
small_array!(18 uniform18);
small_array!(19 uniform19);
small_array!(20 uniform20);
small_array!(21 uniform21);
small_array!(22 uniform22);
small_array!(23 uniform23);
small_array!(24 uniform24);
small_array!(25 uniform25);
small_array!(26 uniform26);
small_array!(27 uniform27);
small_array!(28 uniform28);
small_array!(29 uniform29);
small_array!(30 uniform30);
small_array!(31 uniform31);
small_array!(32 uniform32);
#[cfg(test)]
mod test {
use super::*;
#[test]
fn shrinks_fully_ltr() {
fn pass(a: [i32; 2]) -> bool {
a[0] * a[1] <= 9
}
let input = [0..32, 0..32];
let mut runner = TestRunner::deterministic();
let mut cases_tested = 0;
for _ in 0..256 {
// Find a failing test case
let mut case = input.new_tree(&mut runner).unwrap();
if pass(case.current()) {
continue;
}
loop {
if pass(case.current()) {
if !case.complicate() {
break;
}
} else {
if !case.simplify() {
break;
}
}
}
let last = case.current();
assert!(!pass(last));
// Maximally shrunken
assert!(pass([last[0] - 1, last[1]]));
assert!(pass([last[0], last[1] - 1]));
cases_tested += 1;
}
assert!(cases_tested > 32, "Didn't find enough test cases");
}
#[test]
fn test_sanity() {
check_strategy_sanity([(0i32..1000), (1i32..1000)], None);
}
}